Lesson 4: Water Supplies

Lesson Index
Env115 Frontpage
Subjects & Courses

°Introduction to Groundwater
°Iron and Manganese Removal
°Corrective Treatment
°Hydrogen Sulfide
°Turbidity Removal

  Printable Version of Lesson 3


Lesson 3: 
Treatment Well 


Turbidity Removal

In this section we will answer the following questions:

  • What is turbidity?
  • How is turbid water treated?


Cloudy Water

Turbidity is the cloudy appearance of water caused by small particles suspended in the water.  Water with little or no turbidity will be clear.  A maximum level of 0.5 NTU is allowable in groundwater. 

Excess turbidity levels can occur in groundwater found in limestone and unconsolidated rock formations.  In addition, many springs experience fluctuating levels of turbidity and extensive monitoring of the water is required.  All springs must be equipped
with a constant monitoring turbidimeter to shut off spring pump operation if turbidity levels are excessive.



Filtration alone will not remove the turbidity and bacteria in groundwater.  In addition, a coagulation step is necessary to concentrate the fine particles into floc, which can be removed by filters. 

Coagulation involves the addition of chemicals called coagulant aids.  Alum or polymers are often used for coagulation.  Then the water is allowed to settle for one to two hours, which gives the coagulant aids time to concentrate the water's suspended particles into floc.  The settling period also gives the chlorine contact time.  The final step is filtration to remove the floc.  Rapid sand filters provide the best treatment. 

A treatability study is suggested for any groundwater reading treatment for turbidity removal.  This study will ensure the facilities will perform properly once constructed.  The Health Department will not approve this type of source and treatment as a single water source because of the unpredictability of groundwater quality.


Part 7: Filters